Most likely caused by smacking a hard round object with an object made of softwood.

Bats will break eventually - some are lucky to last a season the way some people bat!
3 seasons isn't too young for a cricket really these days - I'd say it's pretty expected to have some surface cracks. It doesn't look too bad - what I tend to do for my clean ups if there are cracks like that can't be opened up is give it a bit of a sand, apply some CA glue then resand after it's started curing. Just seals the crack in hope that it prevents it from cracking up more from there. Keep an eye on the ones at the edge, and the middle ones aren't too much to worry about if they're not super deep!